Process for continuously drying and stabilizing pasta and the like, and apparatus for implementing the process

ABSTRACT

A process for continuously drying and stabilizing pasta and the like in which the product to be treated is subjected to a succession of cycles each including of an intense drying stage and a stabilizing stage for cooling in which the air temperature exceeds the dew point, characterized in that during the stabilizing phase the pasta is ventilated, whereby the ventilated air is indirectly heated or cooled by a conditioning fluid to create and maintain in the chamber the temperature and humidity required to the particular stabilization treatment.

This invention relates to a process for continuously drying andstabilizing pasta and like, and an apparatus for implementing theprocess.

Production processes for pasta generally comprise a final drying stagein which the water content of the pasta is reduced to an average of10-13% by weinght, to ensure a long product shelf life. This dryingstage does not result in uniform drying throughout the entire pastamass, but involves water evaporation from its outer surface andmigration of further water from the pasta interior to the surfacelayers, to recreate the equilibration which the surface evaporationalters.

This drying is sometimes done slowly so as not to create mechanicalstresses within the pasta which could result in product damage duringits subsequent packaging, storage, transportation and cooking, but inthis case the drying time is excessively long and the plant is verylarge, with high operating costs.

The pasta drying can also be done at a high rate, but alternating thedrying stages with stabilization stages, in which the pasta, the surfaceof which has dried to an extent greater than that desidered, issubjected to a surface remoisturizing stage which restores theplasticity lost during the preceding rapid drying stage.

In Italian Application Nr. 41583 A/86 the pasta is remoisturized afteran intense drying stage, by spraying water into a part of the drier.However with this method there is the danger of wetting the product tobe treated.

It is also known to remoisturize the pasta after an intense dryingstage, by injecting steam. This method requires a steam generator, thecost of which is added to the plant cost, and also involves an energycost in its operation.

It also carries the danger of introduction of chlorine compounds intothe drier because of possible imperfect operation of the water treatmentplant used for generating the steam. This can result in rapid corrosionof the stainless steel used in the drier construction.

Finally, the steam produces a temperature increase in the pasta, whereasin this stage a temperature reduction would be desiderable to avoid anexcessive heat load for the final cooler and a corresponding increase inenergy costs.

In addition to these drawbacks of known pasta stabilization processes,it should be noted that generally a single drying and stabilizationcycle is insufficient, but instead several cycles are required in whichthe pasta is subjected to alternations of only a limited extent, inorder as far as possible to liken the forced drying process to thenatural tendency of the pasta to continuously vary its moisture content.Moreover, this alternation of drying and remoisturizing stages meansthat different climates must be provided, with obvious high installationand running costs.

DE-B-1.142.794 describes a tunnel dryer for long pasta goods with aconveyor tunnel subdivided into ventilated areas and not ventilatedareas.

U.S. Pat. No. 2,790,250 relates to an automatic and continuous processfor drying alimentary pasta goods in which the goods are continuouslyand alternatively conveyed through areas of circulating heated air and"dead" or not circulating air areas.

FR-A-2.562.647 describes a drying process for pasta comprisingadditional phases of ventilations, of resting and of cooling.

U.S. Pat. No. 2,732,627 relates to the drying of alimentary pastacomprising a drying chamber in which ventilated zones are alternativelyfollowed by zones having still air therein.

According to the invention, a satisfactory continuous drying andstabilization of pasta and the like is achieved by a process asdescribed in claim 1.

To implement the aforedescribed process the invention uses an apparatusas described in claim 5.

Some preferred embodiments of the present invention are describedhereinafter with reference to the accompanying drawings in which:

FIG. 1 is a schematic section through a first embodiment of theapparatus according to the invention;

FIG. 2 shows the outline scheme of the circuit for air conditioning theenvironment in which an intense drying stage of the process according tothe invention takes place;

FIG. 3 is a schematic section through a different embodiment of theapparatus according to the invention; and

FIG. 4 is a schematic section through a further embodiment of theapparatus according to the invention.

As can be seen from FIG. 1, the apparatus of the invention, in theembodiment shown in FIG. 1, comprises a plurality of environmentsconsisting respectively of intense drying chambers 2 and remoisturizingchambers 4. The chambers are positioned alternately along an ideal pathwhich the pasta 6 is to undergo from the commencement to the end oftreatment. For this pourpose, each chamber 2,4 is traversed by aconveyor belt 8, the ends of which emerge from the opposing walls of thechamber, the conveyor belts of two successive chambers being connectedtogether by further conveyor connection belts 10.

Each chamber 2,4 houses a bank of fins 12 and a fan 14, facing it, forcirculating the conditioning air. The bank of fins 12 is associted witha pipe 16 which extends into an external circuit comprising a heatexchanger 18, a three-way valve for controlling the fluid flow ratethrough the pipe 16, and a control valve 22 for controlling the entry ofcold water into the heat exchanger 18.

In the chamber 2,4 there are also provided two probes 24 and 26 formeasuring respectively the temperature and humidity of the air withinthe chamber, a further probe 28 being positioned in the pipe 16 tomeasure the temperature of the condioning fluid at the entry to the bankof fins 12.

The output signals from the three probes 24,26 and 28 are fed to atemperature controller, preferably a computer 30, the purpose of whichis to control both the three-way valve 20 and the control valve 22.

The operation of the apparatus of the invention, with reference forexample to the stabilization chamber 4, is as follows:

the temperature and humidity measured by the two probes 24 and 26 arefed to the processor 30 and compared with the preset values memorizedtherein. Using these data, the processor 30 by means of a suitablealgorithm calculates the dew point, this being the minimum allowabletemperature for the water circulating through the pipe 16 of the bank offins 12. The processor 30 also compares the temperature measured by theprobe 28 immediately upstream of the bank of fins 12 with the calculateddew point and, using a suitable algorithm, generates a signal to be fedto the control valve 22 to regulate the entry of cold water into theheat exchanger 18. In this manner it is possible to create and maintainin the chamber 4 the temperature and humidity required for theparticular stabilization treatment.

An analogous circuit for the chamber 2 aslo enables the temperaturerequired for that treatment stage to be obtained.

In this manner the pasta 6 to be treated passes through the variousenvironments one after another, and at each passage is subjected to anintense drying stage which reduces the average moisture content to belowthe final desired value, with a greater internal water content and alesser surface water content, and then to remoisturizing stage obtainedby cooling the pasta with the air temperature exceeding the dew point toprevent condensation of environmetal moisture.

The pasta is therefore subjected to an alternation of climates whichincreasingly approach the final conditions to be attained, so that ontermination of the process the pasta is completely dried and stabilized.

The aforedescribed system enables the climatic conditions within eachchamber to be controlled with satisfactory precision, but has obvioushigh instalation and operating costs because of the need for a pluralityof separate environments and a separate air conditioning system for eachenvironment.

In the embodiment shown in FIG. 3 there is a single tunnel 32 traversedby a conveyor belt 8 on which the pasta 6 to be treated is placed.

The tunnel contains, in the direction of its lenght, a plurality ofbanks of fins 12, each of which is associated with a fan 14 and a pipe16 connected to an external circuit, of the type already described withreference to FIG. 2. The purpose of the succession of banks of fins 12is to create within the tunnel alternate drying and moisturizingregions, and are therefore associated with heating and cooling circuitsrespectively.

Consequently the pasta 6 transported by the belt 8 along the tunnel 32passes alternately through heated and cooled regions and is subjected toa succession of cycles each consisting of a drying stage and amoisturizing stage which cause it to be perfectly dry and stabilized anleaving the tunnel 32.

This embodiment is more advantageous than the preceding because there isonly one treatment chamber, with resultant lesser installation andoperating costs. However the lack of precise separation between theregions of different climate makes it more difficult to control theclimatic conditions of each region.

The embodiment shown in FIG. 4 combines the merits of the two precedingembodiments, while at the same time overcoming their drawbacks. In thisembodiment the apparatus comprises two separate mutually facing chambersconsisting of an intense drying chamber 2 and a remoisturizing chamber4. The drying chamber 2 is provided in that wall 33 distant from thechamber 4 with an entry aperture 34 for a conveyor belt for the pasta 6to be treated, and is also provided with a plurality of apertures 36 inthat wall 38 facing the chamber 4.

Likewise the chamber 4 is provided in that wall 40 facing the wall 8with a plurality of apertures 42 facing the corresponding apertures 36of said wall 38, for the passage of a plurality of other conveyor belts8, and is also provided in the opposing wall 44 with an aperture 46 forthe passage of an exit conveyor belt 8".

Both the chambers 2,4 are also provided with a bank of fins 12,12' and afan 14,14' facing it, for circulating the conditioning air.

The bank 12 is associated with a conventional heating fluid circuit 16,and the bank 12' is associated with a cooling fluid circuit 16'.

The operation of this embodiment of the apparatus according to theinvention is as follows:

the pasta 6 to be dried, conveyed by the conveyor belt 8', enters thedrying chamber 2, in which the climatic conditions favouring this dryinghave been created. As the same conveyor belt 8' then enters theremoisturizing chamber 4, the pasta 6 already partly dried on itssurface is subjected to surface remoisturizing to complete the firstcycle. The same pasta 6 then leaves the chamber 4 to re-enter thechamber 2, in which it is subjected to its next drying stage beforere-entering the chamber 4, where it undergoes its next stabilizationstage, and so on until it is transferred by the conveyor belt 8" to theoutside on termination of the treatment.

This embodiment has the advantages deriving from a small number (two) ofair conditioning environments, ie low installation and operating costs,and also the advantages deriving from completely separate environments,ie high reliability in controlling the climatic conditions in eachenvironment.

Independently of the embodiment used, the humidity control is effectedon the basis of traditional criteria.

We claim:
 1. A process for continuously drying and stabilizing a pastaproduct comprising subjecting said pasta product to a plurality ofcycles, each comprising an intense drying stage in which said productreaches a prefixed value of temperature and humidity and a stabilizingstage for cooling said product in which the air temperature exceeds thedew point and said product is kept at the same value of humidity of saidprevious intense drying stage, wherein said pasta product is ventilatedduring said stabilizing phase and whereby ventilated air is indirectlytreated by a conditioning fluid to create and maintain a temperature andhumidity required for a particular stabilization treatment.
 2. Anapparatus for implementing the process a claimed in claim 1, comprisingmeans for transferring said pasta product from cycle to cycle comprisinga bank of fins traversed by a pipe through which conditioning fluid iscirculated, a fan for circulating air within each stage for grazing saidbank of fins, a temperature sensor for said conditioning fluid passingthrough said pipe, a second temperature sensor for said air, a humiditysensor for said air, and a temperature controller for handling signalsreceived from said first and second temperature sensors for controllingthe temperature and flow rate of said conditioning fluid in relation toa preset climate to be created for each stage.
 3. An apparatus asclaimed in claim 2 further comprising a plurality of separateenvironments having preset climates therein connected together by meansfor transferring said pasta product from one environment to anotheralong a predetermined path which traverses said environments, in which adrying climate and a stabilizing climate are created alternately.
 4. Anapparatus as claimed in claim 2 further comprising a tunnel traversedlongitudinally by conveying means for the pasta product and wherein saidtunnel houses a plurality of drying and stabilizing units locatedalternately along a direction of advancement of said pasta product. 5.An apparatus as claimed in claim 2 comprising two separate environmentswherein said first environment contains a drying climate and whereinsaid second environment contains a stabilizing climate, saidenvironments being connected together by a plurality of conveying meansfor the pasta product, whereby said product passes alternately from oneenvironment to the other.
 6. An apparatus as claimed in claim 2, whereinsaid temperature controller is a microprocessor.
 7. An apparatus asclaimed in claim 2, wherein said pipe which traverses said bank of finsextends external to said environment into a circuit comprising membersfor varying temperature flow rate of said conditioning fluid under thecontrol of said temperature controller.